"Just do the damn thing," she tells CNBC Make It. "There's a conception out there: Oh, I have to have $100,000 to invest or $50,000 or $10,000. Just start where you are."

The ultimate goal, she says, "is to be saving and investing 20% of your take home pay." But you don't have to start with that much right away: "I know it's a lot, so start with 1%, start with 2%." Then, aim to gradually increase that amount over time.

Failing to invest is like letting money fall out of your wallet every day, she explains. When you keep money in a regular savings account, your annualized return is tiny — most people earn far less than 2% on their savings accounts. But if you put your money to work in a diversified portfolio, the returns have historically been about 6%.

And, if you invest in equities, or stocks, "it's been about a 9.5% annualized returns," Krawcheck says. Stocks come with more risk than bonds and cash but have the potential for higher returns. Whether you choose to invest in a diversified portfolio or stocks, the returns they can offer "is a lot more than the close-to-nothing that you get from saving — and the nothing that you get from spending," she says.

The easiest way to work your way up to investing 20% of your income is to have a percentage of your paycheck go straight into your employer-sponsored 401(k), "particularly if there's a company match," Krawcheck says.

With a match your employer will make a contribution to your 401(k) that is the same as your contribution, up to a certain amount. For example, if you choose to put 4% of your salary directly into your account, your employer will put that same amount in as well, in effect doubling your contribution.

"If a company is giving you 25 cents to every dollar that you're putting in, that's a 25% return, which is pretty rare to get in the stock market and very rare to get in any kind of diversified investment portfolio — and it comes with with no risk."

If you don't have access to a 401(k) plan, you can put your money in other retirement accounts, such as a Roth IRA or traditional IRA, which also offer major tax benefits like a 401(k).